1. Field of the Invention
The present invention relates to a method for forming a monomolecular film of a clathrate complex compound and a built-up film thereof and to a recording medium and a method utilizing a chemical or physical change in such a film for recording.
2. Description of the Prior Art
Recent progress of technology in organic materials is remarkable, resulting in fabrication or proposal of various devices, for example, display or recording media, provided with films of organic materials.
Known display media utilizing organic compounds for display layers include, for example, those using organic compounds (electrochromic materials) which develop color on undergoing oxidation-reduction reaction and those using fluorescent organic compounds.
Some types of display media using electrochromic materials have been proposed (e.g. Japanese Patent Laid-open Publication Nos. 71380/73, 32958/75, 63950/75, and 136000/75). These types of display media according to the prior art all relate to the so-called organic-EC (electrochromic) display device that operates with a voltage applied across a color-forming layer made of a solution of an electrochromic material viologen derivative in a suitable electrolyte. A colored pattern is formed in this process according to the pattern of an electrode which is a component of the organic-EC device.
However, the electrochromic material in these organic-EC elements, because it is dissolved in an electrolyte, is considerably free to move and is inferior in responsiveness (the time from voltage application to color formation or disappearance). Thus, these organic-EC devices cannot serve as high-density color display devices. In addition these organic-EC elements are short in memory time and are inferior in reversibility (color formation .rarw..fwdarw. color disappearance) because a colored substance deposited on electrodes is redissolved in the solvent (electrolyte). In order to eliminate these drawbacks of the prior art organic-EC devices, the electrochromic material is required to adhere in a highly ordered state onto the patterned electrodes of the display element.
Some types have been proposed also of luminescent display devices using fluorescent organic compounds (e.g. Japanese Patent Laid-Open Publication Nos. 35587/77 and 172891/83). These devices according to the prior art relate all to the so-called EL (electroluminescence) display device that emits light on voltage application across a luminescent display layer made of an electroluminescent compound. In particular, the device disclosed in the above Laid-Open Publication No. 35587/77 is constructed by forming a monomolecular film or monomolecular-layer built-up film of a derivative of anthracene, pyrene, or perylene having hydrophilic and hydrophobic substituents on suitable positions, on an electrode plate, and forming another electrode on the above film. It is desirable for achieving a high degree of resolution with this type of display device that luminescent molecules in the film be maintained in a highly ordered distribution state. However, the above-mentioned derivatives of anthracene and other compounds are disadvantageous in that cautions and complicated operations are necessary for producing highly ordered monomolecular films or monomolecular-layer built-up films of these derivatives [Thin Solid Film, Vol. 99, pp. 71-79 (1983)].
Optical recording media using thin films of organic compounds as recording layers have been disclosed, for example, in Japanese Patent Laid-Open Publication Nos. 16948/81 and 125246/83. These Patent Application both relate to laser recording media in which recording layers of organic coloring matter are used for recording and reproducing with laser beams. In particular, the medium disclosed in the above Laid-Open Publication No. 125246/83 comprises a thin recording film of a cyanine pigment represented by the following general formula (I): ##STR1## This recording film is formed by applying a solution of the cyanine pigment on a plastic substrate by means of a spinner coater to a thickness of up to 1000 .ANG., e.g. 300 .ANG.. When the distribution or orientation of molecules in the film is random, the light incident on the film is scattered in the film and the degree of chemical reaction caused by light irradiation varies from time to time of the irradiation. Therefore, it is desirable for recording media that the distribution and orientation of the molecules forming the recording film be uniform, and it is requested for high density recording that the recording film be as thin as possible. However, this film when formed by coating cannot be made thinner than about 300 .ANG. and the random distribution or orientation of molecules in the film is inevitable.
Meanwhile, Japanese Patent Laid-Open Publication Nos. 42229/81 and 43220/81, and other literature have disclosed that built-up films of diacetylene compounds already proposed as a resist material which exhibits a high quantum yield and has superior resolving power are applicable not only as a resist material but also to thin film electro-optical devices, electro-acoustic devices, piezo-pyroelectric devices, etc.
More recently, improvements of a method for producing built-up films of diacetylene compounds have been disclosed in Japanese Patent Laid-Open Publication No. 111029/83. Diacetylene compound built-up films formed on substrates according to these inventions are irradiated with ultraviolet rays either without masking to form diacetylene compound polymer films or with masking to cause the polymerization partly, and the unpolymerized portions are removed to form patterns, thereby being used for thin film optical devices and integrated circuits.
However, these patent applications are all limited to diacetylene compounds and do not describe whether information once recorded in these films used for film optical devices can be erased or not.